Navegando por Autor "Grams, Thorsten E. E."
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Item Analysis of competition effects in Mono- and mixed cultures of juvenile beech and spruce by means of the plant growth simulation model PLATHO.(2006) Gayler, Sebastian; Grams, Thorsten E. E.; Kozovits, Alessandra Rodrigues; Winkler, J. B.; Luedemann, Gustavo; Priesack, E.Inter- and intra-specific competition between plants for external resources is a critical process for plant growth in natural and managed ecosystems. We present a new approach to simulate competition for the resources light, water, and nitrogen between individual plants within a canopy. This approach was incorporated in a process-oriented plant growth simulation model. The concept of modelling competition is based on competition coefficients calculated from the overlap of occupied crown and soil volumes of each plant individual with the occupied volumes of its four nearest neighbours. The model was parameterised with data from a two-year phytotron experiment with juvenile beech and spruce trees growing in mono- and mixed cultures. For testing the model, an independent data set from this experiment and data from a second phytotron experiment with mixed cultures were used. The model was applied to analyse the consequences of start conditions and plant density on plant-plant competition. In both experiments, spruce dominated beech in mixed cultures. Based on model simulations, we postulate a large influence of start conditions and stand density on the outcome of the competition between the species. When both species have similar heights at the time of canopy closure, the model suggests a greater morphological plasticity of beech compared with spruce to be the crucial mechanism for competitiveness in mixed canopies. Similar to the experiment, in the model greater plasticity was a disadvantage for beech leading to it being outcompeted by the more persistent spruce.Item Combining d13C and d18O analyses to unravel competition, CO2 and O3 effects on the physiological performance of different-aged trees.(2007) Grams, Thorsten E. E.; Kozovits, Alessandra Rodrigues; Häberle, Karl Heinz; Matyssek, Rainer; Dawson, Todd E.Combined d13C and d18O analyses of leaf material were used to infer changes in photosynthetic capacity (Amax) and stomatal conductance (gl) in Fagus sylvatica and Picea abies trees growing under natural and controlled conditions. Correlation between gl and d18O in leaf cellulose (d18Ocel) allowed us to apply a semi-quantitative model to infer gl from d18Ocel and also interpret variation in d13C as reflecting variation in Amax. Extraction of leaf cellulose was necessary, because d18O from leaf organic matter (d18OLOM) and d18Ocel was not reliably correlated. In juvenile trees, the model predicted elevated carbon dioxide (CO2) to reduce Amax in both species, whereas ozone (O3) only affected beech by reducing CO2 uptake via lowered gl. In adult trees, Amax declined with decreasing light level as gl was unchanged. O3 did not significantly affect isotopic signatures in leaves of adult trees, reflecting the higher O3 susceptibility of juvenile trees under controlled conditions. The isotopic analysis compared favourably to the performance of leaf gas exchange, underlining that the semi-quantitative model approach provides a robust way to gather time-integrated information on photosynthetic performance of trees under multi-faced ecological scenarios, in particular when information needed for quantitative modelling is only scarcely available.Item Nutrient contents and eYciencies of beech and spruce saplings as inXuenced by competition and O3/CO2 regime.(2009) Rodenkirchen, Hermann; Göttlein, Axel; Kozovits, Alessandra Rodrigues; Grams, Thorsten E. E.Saplings of Fagus sylvatica and Picea abies were grown under conditions of intra and interspeciWc competition in a 2-year phytotron study under combinations of ambient and elevated ozone (+O3 which is 2 £ O3, but <150 nl l¡1) as well as carbon dioxide concentrations (+CO2 which is amb. CO2 + 300 l CO2 l¡1) in a full factorial design. Saplings were analysed for various mineral nutrients in diVerent plant organs as well as biomass production and crown development. The study was based on the assumption that nutritional parameters important for growth and competitiveness are aVected by stress defence under limiting nutrient supply. The hypotheses tested were (1) that nutrient uptake-related parameters (a) as well as eYciencies in nutrient use for above-ground competition (b) of beech rather than spruce are impaired by the exposure to elevated O3 concentrations, (2) that the eYciency in nutrient uptake of spruce is enhanced by elevated CO2 concentrations in mixed culture, and (3) that the ability to occupy above-ground space at low nutrient cost is co-determinant for the competitive success in mixed culture. Clear nitrogen deWciencies were indicated for both species during the 2-year phytotron study, although foliar nitrogen-biomass relationships were not so close for spruce than for beech. O3 stress did not impair nutrient uptake-related parameters of beech; thus hypothesis (1a). was not supported. A negative eVect of elevated O3 (under amb. CO2) on the N and P based eYciencies in above-ground space occupation (i.e. lower crown volume per unit of N or P invested in stems, limbs and foliage) of beech supported hypothesis (1b). It appeared that ozone stress triggered a nutrient demand for stress defence and tolerance at the expense of above-ground competition (trade-oV). Crown volume of beech under O3 stress was stabilized in monoculture by increased nutrient uptake. In general, the +CO2-treatment was able to counteract the impacts of 2 £ O3. Elevated CO2 caused lower N and S concentrations in current-year foliage of both tree species, slightly higher macronutrient amounts in the root biomass of spruce, but did not increase the eYciencies in nutrient uptake of spruce in mixed culture. Therefore hypothesis (2) was not supported. At the end of the experiment spruce turned out to be the stronger competitor in mixed culture as displayed by its higher total shoot biomass and crown volume. The amounts of macronutrients in the above-ground biomass of spruce individuals in mixed culture distinctly exceeded those of beech, which had been strongly reduced by interspeciWc competition. The superior competitiveness of spruce was related to higher N and P-based eYciencies in aboveground space occupation as suggested in hypothesis (3).